Modern electronic devices, such as microprocessors, often include a complex matrix of logic gates arranged to perform particular tasks and functions. These logic gates are often interconnected in two parallel arrangements, one arrangement for operation, and another arrangement for testing circuit functionality. Linking a plurality of latches together into a “scan chain” is one popular method of arranging logic units for functional/operational testing. One skilled in the art will appreciate that there are a wide variety of ways to arrange circuit components that facilitate testing. As used herein, “scan chain” refers generally to an arrangement of logic units coupled together for testing.
There are also a number of popular methods to generate test data to apply to the scan chains, as will be understood to one skilled in the art. In many manufacturing environments, LBIST (Logic Built-In Self Test) is the primary test mechanism to detect non-array manufacturing defects, including both static and dynamic defects. LBIST is also a useful tool to study hardware power and frequency characteristics.
However, as the transistor count increases in modern complex chips, the power generated during a full-chip LBIST scan can become unreasonably high, exceeding tolerable levels. Further, high power dissipation and high di/dt cause unreliable LBIST results and, therefore, hardware reliability issues and difficulty in correlating LBIST with functional (performance) tests.
Conventional approaches to addressing high LBIST power and di/dt suffer from disadvantages. For example, in one approach, slowing the LBIST scan rate reduces di/dt, but increases overall test time. Longer testing time leads to higher manufacturing and testing costs. In another approach, reducing the scan load, scanning at full-load with less-random data, or removing the scan load altogether, reduces LBIST power and di/dt, but also reduces transition (alternating current (AC)) coverage. Reduced AC coverage results in a higher AC defect escape rate, reducing equipment reliability.
Therefore, there is a need for a system and/or method for LBIST testing that addresses at least some of the problems and disadvantages associated with conventional systems and methods.